Battery

ABSTRACT

An alkaline battery has a cathode including a hydrogen absorbing material and an anode including zinc free of lead, mercury, or cadmium.

TECHNICAL FIELD

[0001] This invention relates to batteries.

BACKGROUND

[0002] Batteries, such as primary alkaline batteries, are commonly usedas energy sources. Generally, alkaline batteries include a cathode, ananode, a separator, and an electrolytic solution. The cathode caninclude an active material, such as manganese dioxide or nickel oxide,carbon particles that enhance the conductivity of the cathode, and abinder. The anode may be, for example, a gel including zinc particles asthe active material. The separator is disposed between the cathode andthe anode. The electrolytic solution can be, for example, a hydroxidesolution that is dispersed throughout the battery.

[0003] Desirable primary alkaline batteries have a zinc anode thatgenerates little hydrogen. Typically, primary batteries use amalgamatedzinc anodes. Mercury added to the zinc helps decrease the amount ofhydrogen generated from, for example, water in contact with the zinc.Hydrogen generation in the anode can cause pressure to build up in thebattery which can lead to leaks.

SUMMARY

[0004] The invention features a primary alkaline battery including azinc anode free of lead, mercury, or cadmium. The cathode is ahydrogen-absorbing cathode material. The hydrogen-absorbing cathodematerial presently absorbs hydrogen at a faster rate thanelectrochemically-produced manganese dioxide. For example, thehydrogen-absorbing cathode material absorbs at least 20% more hydrogenthan an equivalent amount of electrochemically-produced manganesedioxide within an equivalent time interval.

[0005] By eliminating added lead, mercury, or cadmium from the anode, asafer, more environmentally friendly battery can be produced. The zincfree of lead, mercury, or cadmium is free of added lead, mercury, orcadmium. The zinc contains less than 100 ppm, preferable less than 25ppm, and more preferably less than 5 ppm of lead, mercury or cadmium.Elimination of a substantial weight and volume of mercury in particularallows a higher gravimetric and volumetric energy density to beachieved. Primary batteries containing electrochemically-producedmanganese dioxide (EMD) cathodes and zinc anodes free of lead, mercury,or cadmium suffer from increased zinc gassing compared to batteries thatcontain mercury, lead or cadmium in the anode. The increased gassingcans cause the battery to leak or rupture. By replacing the EMD cathodewith another cathode material having higher hydrogen absorption ratethan EMD, the cathode can absorb the hydrogen and reduce the incidenceof leakage and rupture. The hydrogen-absorbing cathode material canreduce pressure build-up within the battery that can be produced by zincfree of lead, mercury, or cadmium.

[0006] In one aspect a primary alkaline battery including a cathode, ananode, a separator, and an alkaline electrolyte. The cathode includes ahydrogen-absorbing cathode material. The anode includes zinc free oflead, mercury, or cadmium.

[0007] In another aspect, the invention features a method ofmanufacturing a primary alkaline battery. The method includes assemblinga cathode, an anode, a separator, and an alkaline electrolyte to formthe alkaline battery. The cathode includes a hydrogen-absorbing cathodematerial and the anode includes zinc free of lead, mercury, or cadmium.

[0008] In another aspect, the invention features a primary alkalinebattery including a cathode including an active material that absorbshydrogen more rapidly than an equivalent amount ofelectrochemically-produced manganese dioxide within an equivalent timeinterval, an anode including zinc free of lead, mercury, or cadmium, andan alkaline electrolyte.

[0009] The hydrogen-absorbing cathode material can include a nickeloxyhydroxide, a copper oxide, a chemically-produced manganese oxide, asilver oxide, a barium permanganate or a silver permanganate. The methodalso includes forming an anode including a zinc free of lead, mercury,or cadmium.

[0010] Other features and advantages of the invention will be apparentfrom the description and drawings, and from the claims.

DETAILED DESCRIPTION

[0011] Referring to the FIG. 1, battery 10 includes a cathode 12, ananode 14, a separator 16 and a cylindrical housing 18. Battery 10 alsoincludes current collector 20, seal 22, and a negative metal top cap 24,which serves as the negative terminal for the battery. The cathode is incontact with the housing, and the positive terminal of the battery is atthe opposite end of the battery from the negative terminal. Anelectrolytic solution is dispersed throughout battery 10. Battery 10 canbe, for example, an AA, AAA, AAAA, C, or D battery.

[0012] Cathode 12 includes a hydrogen-absorbing cathode material, carbonparticles, and a binder. The hydrogen-absorbing cathode material absorbshydrogen at a rate faster than an equivalent amount ofelectrochemically-produced manganese dioxide within an equivalent timeinterval. The hydrogen-absorbing cathode material absorbs at least 20%more, preferably at least 30% more, and more preferably 40% morehydrogen than an equivalent amount of electrochemically-producedmanganese dioxide within an equivalent time interval. Thehydrogen-absorbing cathode material can absorb hydrogen at a rate of 1.2to 100, preferably 1.3 to 90, and more preferably 1.4 to 88 times therate of hydrogen absorption of electrochemically-produced manganesedioxide at the same temperature. The electrochemically-producedmanganese dioxide can be produced by the method described, for example,in U.S. Pat. No. 5,698,176, or obtained commercially from, for example,Delta E.M.D. (Pty) Ltd. (Nelspruit, South Africa), or Kerr-McGeeChemical Co. (Oklahoma City, Okla.).

[0013] The cathode material can be a nickel oxyhydroxide, a silveroxide, a copper oxide, a chemically-produced manganese dioxide, a bariumpermanganate, or a silver permanganate. Nickel oxyhydroxide can beformed by oxidation of Ni(OH)₂ as described, for example, in U.S. Pat.No. 3,911,094. Copper oxide can be produced by thermal decomposition ofCuCO₃ or Cu(NO₃)₂. Chemically-produced manganese dioxide (CMD) can beproduced by oxidation of Mn²⁺ using ClO₃ ⁻ or S₂O₈ ²⁻ either in thepresence or absence of a substrate. Silver oxide can be prepared bytreating AgNO₃ with sodium hydroxide and then gently heating theinsoluble precipitate. Barium permanganate can be prepared chemically bytreating barium chloride with silver permanganate or electrochemicallyas described in Zadikashvili et al., Elektrokhim. Margastsa, 3:212(1967). Silver permanganate can be prepared by treating potassiumpermanganate with silver nitrate.

[0014] Distributors of the cathode materials or starting materials formaking the cathode material include HC Starck, JMC Tanaka Chemical Corp.(Fukui, Japan), Johnson-Matthey, Aldrich, Alfa Aesar, or Carus Chemical.Generally the cathode may include, for example, between 80% and 90%, andpreferably between 86% and 88%, of cathode material by weight.

[0015] The carbon particles can be graphite particles. The graphite canbe synthetic or non-synthetic, or a blend of synthetic andnon-synthetic. Suitable graphite particles can be obtained from, forexample, Brazilian Nacional de Grafite (Itapecerica, MG Brazil(MP-0702X)) or Chuetsu Graphite Works, Ltd. (Chuetsu grades WH-20A andWH-20AF) of Japan. The cathode may include for example, between 3% and7%, preferably between 4% and 6.5% carbon particles by weight.

[0016] Examples of binders include polyethylene powders,polyacrylamides, Portland cement and fluorocarbon resins, such as PVDFand PTFE. An example of polyethylene binder is sold under the trade nameCoathylene HA-1681 (available from Hoechst). The cathode may include,for example, between 0.1 percent to about 1 percent of binder by weight.

[0017] Cathode 12 can include other additives. Examples of theseadditives are disclosed, for example, in U.S. Pat. No. 5,342,712, whichis hereby incorporated by reference. Cathode 12 may include, forexample, from about 0.2 weight percent to about 2 weight percent TiO₂.

[0018] The electrolyte solution also is dispersed through cathode 12,and the weight percentages provided above and below are determined afterthe electrolyte solution has been dispersed.

[0019] Anode 14 can be formed of zinc materials that are free of lead,mercury, or cadmium. Preferably, the zinc is free of lead, mercury andcadmium. For example, anode 14 can be a zinc slurry that includes zincmetal particles, a gelling agent, and minor amounts of additives, suchas gassing inhibitor. In addition, a portion of the electrolyte solutionis dispersed throughout the anode.

[0020] The zinc particles can be any of the zinc particlesconventionally used in slurry anodes. Examples of zinc particles includethose described in U.S. Ser. No. 08/905,254, U.S. Ser. No. 09/115,867,and U.S. Ser. No. 09/156,915, which are assigned to the assignee in thepresent application and are hereby incorporated by reference. The anodemay include, for example, between 67% and 71% of zinc particles byweight.

[0021] The anode can include an inorganic gassing inhibitor such asbismuth or indium. The zinc particles can be a zinc alloy containing 25ppm to 1000 ppm indium or 25 ppm to 1000 ppm bismuth. For example, thezinc can contain 150 ppm indium and 200 ppm bismuth.

[0022] The electrolyte can be an aqueous solution of KOH or NaOH. Theelectrolyte can contain 20%-50% by weight alkali hydroxide dissolved inH₂O. The electrolyte can contain 0% to 4% by weight zinc oxide.

[0023] Examples of gelling agents include polyacrylic acids, graftedstarch materials, salts of polyacrylic acids, polyacrylates,carboxymethylcellulose, sodium carboxymethylcellulose or combinationsthereof. Examples of such polyacrylic acids are Carbopol 940 and 934(available from B. F. Goodrich) and Polygel 4P (available from 3V), andan example of a grafted starch material is Waterlock A221 or A220(available from Grain Processing Corporation, Muscatine, Iowa). Anexample of a salt of a polyacrylic acid is Alcosorb G1 (available fromCiba Specialties). The anode may include, for example, from 0.1 percentto about 2 percent gelling agent by weight.

[0024] Gassing inhibitors can be inorganic materials, such as bismuth,tin, and indium. Alternatively, gassing inhibitors can be organiccompounds, such as phosphate esters, ionic surfactants or nonionicsurfactants. Examples of ionic surfactants are disclosed in, forexample, U.S. Pat. No. 4,777,100, which is hereby incorporated byreference.

[0025] Separator 16 can have any of the conventional designs for batteryseparators. In some embodiments, separator 16 can be formed of twolayers of non-woven, non-membrane material with one layer being disposedalong a surface of the other. To minimize the volume of separator 16while providing an efficient battery, each layer of non-woven,non-membrane material an have a basic weight of about 54 grams persquare meter, a thickness of about 5.4 mils when dry and a thickness ofabout 10 mils when wet. In these embodiments, the separator preferablydoes not include a layer of membrane material or a layer of adhesivebetween the non-woven, non-membrane layers. Generally, the layers can besubstantially devoid of fillers, such as inorganic particles.

[0026] In other embodiments, separator 16 includes a layer of cellophanecombined with a layer of non-woven material. The separator also includesan additional layer of non-woven material. The cellophane layer can beadjacent to cathode 12 or the anode. Preferably, the non-woven materialcontains from about 78 weight percent to about 82 weight percent PVA andfrom about 18 weight percent to about 22 weight percent rayon with atrace of surfactant. Such non-woven materials are available from PDMunder the trade name PA25.

[0027] The electrolytic solution dispersed throughout battery 10 can beany of the conventional electrolytic solutions used in batteries.Typically, the electrolytic solution is an aqueous hydroxide solution.Such aqueous hydroxide solutions include potassium hydroxide solutionsincluding, for example, between 33% and 38% by weight percent potassiumhydroxide, and sodium hydroxide solutions.

[0028] Housing 18 can be any conventional housing commonly used inprimary alkaline batteries. The housing typically includes an innermetal wall and an outer electrically non-conductive material such asheat shrinkable plastic. Optionally, a layer of conductive material canbe disposed between the inner wall and the cathode 12. This layer may bedisposed along the inner surface of wall, along the circumference ofcathode 12 or both. This conductive layer can be formed, for example, ofa carbonaceous material. Such materials include LB 1000 (Timcal),Eccocoat 257 (W. R. Grace & Co.), Electrodag 109 (Acheson ColloidsCompany), Electrodag 112 (Acheson) and EB0005 (Acheson). Methods ofapplying the conductive layer are disclosed in, for example, CanadianPatent No. 1,263,697, which is hereby incorporated by reference.

[0029] Current collector 28 is made from a suitable metal, such asbrass. Seal 30 can be made, for example, of nylon.

[0030] Hydrogen absorption tests were conducted on EMD as a control andseven other cathode materials including chemically-produced manganesedioxide, copper (II) oxide, silver (I) oxide, silver (II) oxide, nickeloxyhydroxide, barium permanganate, and silver permanganate. For eachmaterial, 10.56 milli-equivalents of cathode material sufficient toabsorb 118 standard cubic centimeters (scc; measured under standardconditions of 0° C. and 1 atmosphere pressure) of hydrogen were loadedinto a small (e.g.1-2 cc) glass vial which was loosely plugged withpolyester wool. The small glass vial was loaded into foil test bag Thefoil test bag is a plastic/aluminum foil/plastic laminate, as used infood packaging, which is closed by broad heat seals on three sides (e.g.⅜ inch seal width) and is open on the fourth side. The inner plasticlayer is sealable by an impulse type heat sealer, e.g. polyethylene orpolypropylene.

[0031] A flattened metal tube was introduced into the open end of thebag and secured with several strips of masking tape to form a nearlyairtight seal. The tube was attached through an automatic sealingcoupling (Swagelock SS-QC4-D-400 and SS-QC4-B-400) to a H₂ chargingapparatus. The charging apparatus included a closed system containing ahydrogen tank with a regulator set to one atmosphere a pressure gauge tomonitor the system pressure, a ball valve connected to a vacuum pump, a25 mL volume container, and a quick connect fitting that connects to theautomatic sealing coupling. The coupling contains an automatic valvewhich closes upon being disconnected, preventing the H₂ in the bag fromescaping and preventing the atmosphere from entering. Most of the airwas withdrawn from the bag by applying vacuum to the tube (˜28 inchesnegative pressure). From a calibrated volume, 150 to 200 cc of H₂ gas(measured at ambient conditions) was charged into the bag. The bagexpanded to accept the gas. The gas was immediately evacuated, and H₂gas was again charged into the bag. A total of two flushing operationswere executed on the bag. The bag was then charged a final time with150-200 cm³ of H₂. The automatic sealing coupling was disconnected fromthe charging apparatus.

[0032] The bag was immediately sealed on an electric impulse sealer, inthe region close to the taped opening, with three parallel seals,thereby hermetically closing the previously open end of the bag.Scissors were used to cut the section of the bag between the outermostseal and the masking tape, freeing the metal filling tube. Several smallholes were punched in the periphery of the bag in the flat seal area attwo opposite edges. Care was taken not to approach too closely to thecentral, filled portion of the bag.

[0033] The bag was weighed dry. An analytical balance was tared at zerowhile a brass ballast weight of approximately 200 grams suspended fromthe balance was fully immersed in the water. The bag, along with aballast weight attached to one of the small holes at the lower edge ofthe bag, was suspended from the analytical balance and both the bag andthe weight were fully immersed in water. The buoyant weight wasrecorded. The water temperature and ambient pressure were recorded.Using the dry weight, buoyant weight, temperature and pressure, theinitial volume of gas in the bag was calculated. The volume, in standardcubic centimeters (scc; 0° C., 760 mm Hg pressure), was calculated asfollows:

Volume(scc)=(buoyant weight (g)+dry weight (g))×273.16° K/T(° K)×P(mmHg)/760 mm Hg

[0034] Each bag was stored at 55° C., with the exception of the bagcontaining AgMnO₄ which was stored at room temperature. Absorptionmeasurements were carried out by allowing each bag to cool to ambienttemperature for about 1-2 hours prior to weighing by immersing in waterto determine buoyancy as described above. The buoyant weight, watertemperature and ambient pressure were recorded and gas law correctionswere made to determine the quantity of hydrogen gas absorbed after agiven storage period. Any increase in the apparent weight of the bagsignifies a decrease in buoyancy, hence a reduction in volume due to H₂absorption. In general, the H₂ absorption was taken to be 1 cc of H₂ (atambient conditions) for each 1 gram change in weight. This was convertedusing the ideal gas laws to scc of H₂, i.e., at 0° C. and one atmospherepressure.

[0035] The quantities of absorbed H₂ for each of the materials, after 16days and after 35 days, are summarized in Table I. TABLE I HydrogenAbsorbed Hydrogen Absorbed (scc) After 16 (scc) After 35 Material daysat 55° C. days at 55° C. EMD (Kerr-McGee) 0.23 0.35 CMD (Erachem Far2000) 0.67 1.33 CuO (Johnson-Matthey) 0.50 0.74 Ag₂O (Aldrich) 20.3920.51 AgO (Alfa Aesar) 18.85 19.16 NiOOH (Duracell) 13.00 17.77 BaMnO₄(Carus Chemical) 0.33 0.47 AgMnO₄ (Alfa Aesar) 3.17¹ 5.07¹

What is claimed is:
 1. A primary alkaline battery comprising: a cathodecomprising a hydrogen-absorbing cathode material; an anode comprisingzinc free of lead, mercury or cadmium; a separator; and an alkalineelectrolyte.
 2. The battery of claim 1, wherein the zinc is free oflead, mercury and cadmium.
 3. The battery of claim 1, wherein the zincincludes indium or bismuth.
 4. The battery of claim 1, wherein the zincincludes 25 ppm-1000 ppm indium or 25 ppm-1000 ppm bismuth.
 5. Thebattery of claim 1, wherein the zinc includes 25 ppm-1000 ppm indium and25 ppm-1000 ppm bismuth.
 6. The battery of claim 1, wherein thehydrogen-absorbing cathode material includes a nickel oxyhydroxide, acopper oxide, a barium permanganate, a chemically-produced manganesedioxide, a silver oxide, or a silver permanganate.
 7. The battery ofclaim 1, wherein the hydrogen-absorbing cathode material includes anickel oxyhydroxide.
 8. The battery of claim 1, wherein thehydrogen-absorbing cathode material includes a silver oxide.
 9. Thebattery of claim 1, wherein the hydrogen-absorbing cathode materialincludes a silver permanganate.
 10. The battery of claim 1, wherein thehydrogen-absorbing cathode material includes a copper oxide.
 11. Thebattery of claim 1, wherein the hydrogen-absorbing cathode materialincludes a barium permanganate.
 12. The battery of claim 1, wherein thehydrogen-absorbing cathode material includes a chemically-producedmanganese dioxide.
 13. The battery of claim 1, wherein thehydrogen-absorbing cathode material absorbs at least 20% more hydrogenthan an equivalent amount of electrochemically-produced manganesedioxide within an equivalent time interval.
 14. A method ofmanufacturing a primary alkaline battery comprising: assembling acathode comprising a hydrogen-absorbing cathode material, an anodecomprising zinc free of lead, mercury or cadmium, a separator, and analkaline electrolyte to form the alkaline battery.
 15. The method ofclaim 12, wherein the zinc is free of lead, mercury and cadmium.
 16. Themethod of claim 14, wherein the zinc includes indium or bismuth.
 17. Themethod of claim 14, wherein the zinc includes 25 ppm-1000 ppm indium or25 ppm-1000 ppm bismuth.
 18. The method of claim 14, wherein the zincincludes 25 ppm-1000 ppm indium and 25 ppm-1000 ppm bismuth.
 19. Themethod of claim 14, wherein the hydrogen-absorbing cathode materialincludes a nickel oxyhydroxide, a copper oxide, a barium permanganate, achemically-produced manganese dioxide, a silver oxide, or a silverpermanganate.
 20. The method of claim 14, wherein the hydrogen-absorbingcathode material absorbs at least 20% more hydrogen than an equivalentamount of electrochemically-produced manganese dioxide within anequivalent time interval.
 21. A primary alkaline battery comprising: acathode comprising an active material that absorbs hydrogen more rapidlythan an equivalent amount of electrochemically-produced manganesedioxide within an equivalent time interval; an anode comprising zincfree of lead, mercury, or cadmium; and an alkaline electrolyte.
 22. Thebattery claim 21, wherein the actual material includes a nickeloxyhydroxide, a copper oxide, a barium permanganate, achemically-produced manganese dioxide, a silver oxide or a silverpermanganate.
 23. The battery of claim 21, wherein the zinc includeslead, mercury, and cadmium.
 24. The batter of claim 21, wherein theactive material absorbs at least 20% more than an equivalent amount ofelectrochemically-produced manganese dioxide within an equivalent timeinterval.